Interferon is an endogenous protein having an important role in an immune system in mammals, and not only takes a partial role in a nonspecific defense mechanism in a living body but also strongly participates in a specific defense mechanism thereof. Actually, interferon has been used as an agent for treating viral diseases such as hepatitis B and hepatitis C in a clinical field. A low molecular weight organic compound (an interferon-inducing agent) which induces a biosynthesis of the said interferon has been developed as the next generation interferon therapy, including an imidazoquinoline derivative (refer to the patent document 1) and an adenine derivative (refer to the patent documents 2 and 3), and an imidazoquinoline derivative, Imiquimod has been used as an external antiviral agent for genital wart in a clinical field.
On the other hand, T-cell taking a central role in an immune response in a living body is classified into two groups, Th1-cell and Th2-cell, and in a living body of a patient suffering from an allergic disease, an excess amount of cytokines such as interleukin-4 (IL-4) and interleukin-5 (IL-5) is excreted from Th-2 cell, and thus a compound suppressing an immune response of Th2 cell can be expected as an agent for treating allergic diseases.
The above imidazoquinoline derivative and adenine derivative have been known as showing a suppressing activity of production of interleukin-4 (IL-4) and interleukin-5 (IL-5) as well as an inducing activity of interferon, and have been actually known to be effective to an allergic disease also in a model animal.
However, there is such a fear that systemic adverse effects based on the interferon inducing activity would be problem upon using such derivatives as an anti-allergic agent.    [Patent Document 1] U.S. Pat. No. 4,689,338    [Patent Document 2] WO 98/01448    [Patent Document 3] WO 99/28321